Abstract
SummaryHeme is an essential cofactor and alternative iron source for almost all bacterial species but may cause severe toxicity upon elevated levels and consequently, regulatory mechanisms coordinating heme homeostasis represent an important fitness trait. A remarkable scenario is found in several corynebacterial species, e.g. Corynebacterium glutamicum and Corynebacterium diphtheriae, which dedicate two paralogous, heme‐responsive two‐component systems, HrrSA and ChrSA, to cope with the Janus nature of heme. Here, we combined experimental reporter profiling with a quantitative mathematical model to understand how this particular regulatory network architecture shapes the dynamic response to heme. Our data revealed an instantaneous activation of the detoxification response (hrtBA) upon stimulus perception and we found that kinase activity of both kinases contribute to this fast onset. Furthermore, instant deactivation of the PhrtBA promoter is achieved by a strong ChrS phosphatase activity upon stimulus decline. While the activation of detoxification response is uncoupled from further factors, heme utilization is additionally governed by the global iron regulator DtxR integrating information on iron availability into the regulatory network. Altogether, our data provide comprehensive insights how TCS cross‐regulation and network hierarchy shape the temporal dynamics of detoxification (hrtBA) and utilization (hmuO) as part of a global homeostatic response to heme.
Highlights
SummaryHeme is an essential cofactor and alternative iron source for almost all bacterial species but may cause severe toxicity upon elevated levels and regulatory mechanisms coordinating heme homeostasis represent an important fitness trait
Provided that excess heme is toxic to the cells, we wondered which strategy C. glutamicum uses to regulate the balance between its heme utilization and detoxification modules
A wildtype strain of C. glutamicum transformed with plasmids carrying the reporter constructs revealed highly distinct response profiles and a temporal hierarchy in reporter output of the PhmuO and PhrtBA promoters (Fig. 1): While we observed a nearly instant but transient response for the heme detoxification module hrtBA to 4 μM extracellular heme (Fig. 1, red line ), the heme utilization module hmuO displayed higher initial expression levels compared to hrtBA and experienced an expression boost after a delay of about 5 h (Fig. 1, green line )
Summary
Heme is an essential cofactor and alternative iron source for almost all bacterial species but may cause severe toxicity upon elevated levels and regulatory mechanisms coordinating heme homeostasis represent an important fitness trait. Bacterial two-component systems (TCS), consisting of a membrane bound histidine kinase (HK) and a cytoplasmatic response regulator (RR) (Mascher et al , 2006; Zschiedrich et al , 2016), play a central role as transient heme sensor systems in Gram-positive species (Stauff and Skaar, 2009b) This is known from bacteria such as Staphylococcus aureus and Bacillus anthracis , both utilizing the heme sensor system HssRS to react to heme as extracellular stimulus (Stauff and Skaar, 2009a; 2009b). While in C. glutamicum it was suggested that both TCS have partially overlapping regulons, HrrSA was shown to play an important role in in the utilization of heme as an alternative iron source by activating expression of hmuO , whereas ChrSA is crucial for the activation of the hrtBA operon encoding a heme exporter (Frunzke et al , 2011; Heyer et al , 2012). By studying the impact of the iron regulator DtxR on hrrA and hmuO expression at temporal resolution our data as well as the model revealed that DtxR adds an important additional regulatory level ensuring the appropriate timing of heme utilization
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
